Factor Analysis

The lack of a universally accepted definition has not deterred continuous
theorizing and research on the concept of intelligence. The central issue
that has dominated theoretical models of intelligence is the question of
whether it is a single, global ability or a collection of specialized abilities.
This debate, started in England by Charles Spearman, is based on research
that uses the correlations among various measures of abilities and, in particular,
the method of factor analysis, which was also pioneered by Spearman.
As early as 1904, Spearman, having examined the patterns of correlation coefficients
among tests of sensory discrimination and estimates of intelligence,
proposed that all mental functions are the result of a single general
factor, which he later designated g.
Spearman equated g with the ability to grasp and apply relations. He also
allowed for the fact that most tasks require unique abilities, and he named
those s, or specific, factors. According to Spearman, to the extent that performance
on tasks was positively correlated, the correlation was attributable
to the presence of g, whereas the presence of specific factors tended to lower
the correlation between measures of performance on different tasks.
By 1927, Spearman had modified his theory to allow for the existence of
an intermediate class of factors, known as group factors, which were neither
as universal as g nor as narrow as the s factors. Group factors were seen as accounting
for the fact that certain types of activities, such as tasks involving
the use of numbers or the element of speed, correlate more highly with one
another than they do with tasks that do not have such elements in common.
Factor-analytic research has undergone explosive growth and extensive variations and refinements in both England and the United States since the
1920’s. In the United States, work in this field was influenced greatly by Truman
Kelley, whose 1928 book Crossroads in the Mind of Man presented a
method for isolating group factors, and L. L. Thurstone, who by further
elaboration of factor-analytic procedures identified a set of about twelve factors
that he designated as the “primary mental abilities.” Seven of these were
repeatedly found in a number of investigations, using samples of people at
different age levels, that were carried out by both Thurstone and others.
These group factors or primary mental abilities are verbal comprehension,
word fluency, speed and accuracy of arithmetic computation, spatial visualization,
associative memory, perceptual speed, and general reasoning.